Microcomputers generally comprise a processor and memory, the memory including storage locations some of which may be used for holding a sequence of instructions for execution by the processor. When combining memory with a processor on the same chip, problems arise from limited chip area available as well as noise interference which may affect memory of the RAM type where the contents of memory may be affected by unwanted electrical signals. Due to the space requirements of a RAM array, as well as noise sensitivity on-chip memory of substantial memory capacity combined with a processor on the same chip has been in the form of ROM. Any substantial RAM memory facility has been located in an off-chip memory.
It is an object of the present invention to provide a microcomputer with both a processor and at least 1K bytes of RAM on-chip together with isolation regions to protect the RAM from noise due to independent operation of other circuitry on the chip.